Study On Preparation And Electrochemical Performance Of ZIF-67 Derived Bimetallic Composite

In this theise,ZIF-67 was used as the precursor template to prepare nickel-cobalt layered double hydroxide(NiCo-LDH)electrode materials.The synthesis method and doping are improved by compounding and modifying multi-walled carbon nanotubes and designing a one-step water-solvent method.Research on improving the electrochemical performance of electrode materials has been carried out through technical approaches such as mixing different metal elements.The main work carried out is as follows.(1)Compared with the vacuum drying method,the ZIF-67 grain size prepared by the freeze drying method is smaller,the magnetism is weaker,and it is easier to collect.NiCoLDH was prepared with ZIF-67 as the precursor,and NiCo-LDH@NNO-MWCNT electrode material was prepared by compounding it with sodium methylene naphthalenesulfonate modified multi-walled carbon nanotubes(NNO-MWCNT).When the added amount of modified carbon nanotubes is 500 mg,the NiCo-LDH@NNO-MWCNT electrode material shows good electrochemical performance.When the current density is 2A/g,5 A/g,8 A/g and 10 A/g,the specific capacity is 2197.7 F/g,1899.7 F/g,1453.3 F/g and 1236.0 F/g;when the current density is 10 A/g,after 2000 cycles,the cycle efficiency is 60.4%,and it has good cycle stability.(2)A one-step water-solvent method was designed to prepare NiCo-LDH electrode material,and the influence of the addition amount of nickel nitrate hexahydrate,the addition amount of deionized water and the heating reaction time on the electrochemical performance of the electrode material was studied by the controlled variable method.When the addition amount of deionized water is 40 ml,the addition amount of nickel nitrate hexahydrate is 291 mg,and the heating reaction time is 40 min,the electrode material has the highest specific capacity,and the specific capacity is at the current density of 2 A/g,5A/g,8 A/g and 10 A/g.Respectively 1824.7 F/g,1687.3 F/g,1598.7 F/g and 1524.7 F/g;the specific capacity retention rate is 83.6% when the current density is 2-10 A/g;the cycle efficiency is 77.7% after 1400 times of charge and discharge.The electrochemical performance of electrode materials has been greatly improved.(3)Selecting lithium,manganese,and zinc as the doping elements,the metal element doping modification study was carried out for the NiCo-LDH electrode material prepared by the one-step water-solvent method.The prepared lithium,manganese,and zinc modified electrode materials have specific capacities of 1267.3 F/g,1120.7 F/g,and 884.7F/g when the current density is 10 A/g,respectively.The specific capacity of the lithium modified electrode material when the current density is 1 A/g,2 A/g,5 A/g,8 A/g are1517.7 F/g,1438.9 F/g,1354.3 F/g,1318.0 F/g,respectively,the capacity retention rate is83.5%,and the capacity retention after 2000 charge and discharge cycles 58.3%.After metal doping,the overall specific capacity of the electrode material is reduced,and the cycle stability is reduced.Through impedance spectroscopy,it is found that the conductivity and charge transfer efficiency of the electrode material are greatly improved after doping with metal elements,and the material maintains a higher rate performance.